Preventing Carburizing By Copper-plating

Copper-plating has been found effective and must have a thickness
of 0.0005 in. Less than this does not give a continuous coating.
The plating bath used has a temperature of 170 deg.F. A voltage of
4.1 is to be maintained across the terminals. Regions which are
to be hardened can be kept free from copper by coating them with
paraffin before they enter the plating tank. The operation is as
follows:

There are also other methods of preventing case-hardening, one
being to paint the surface with a special compound prepared for
this purpose. In some cases a coating of plastic asbestos is used
while in others thin sheet asbestos is wired around the part to
be kept soft.